Targeted photodynamic therapy using reconstituted high-density lipoproteins as rhodamine transporters

Reconstituted high-density lipoprotein (rHDL) nanoparticles are excellent transporters of molecules and very useful for targeted therapy as they specifically recognize the scavenger receptor, class B1 (SR-B1) that is present on the surface of a wide range of tumor cells. However, they have rarely been employed to transport photosensitizers (PS) for photodynamic therapy (PDT). Rhodamine (R) compounds have been dismissed as useful PSs for PDT due to their low ¹O₂ production, excitation wavelengths with little tissue penetration, and poor selectivity for tumor cells. It was recently demonstrated that when irradiating at 532 nm or with Cerenkov radiation (CR) from a β-emitting radionuclide, R123, R6G, and RB undergo electron transfer reactions (type I reaction) with folic acid. R6G also produces type I reactions with O₂. In this work, the photodynamic effects of the rHDL-R system were evaluated in vitro. rHDL nanoparticles loaded with R123, R6G, and RB were synthesized, and the PS was internalized into T47D tumor cells. When cells were irradiated with a 532-nm laser in the presence of an rHDL-R systems, a cytotoxic photodynamic effect was obtained in the order R6G > R123 > RB. In the presence of CR from a ¹⁷⁷Lu source, cytotoxicity showed the order R6G > RB > R123. The higher cytotoxicity induced by R6G in both cases corresponds to higher cellular internalization and larger production of type I and II reactions. Thus, in this work, it is proposed that rHDL-R/¹⁷⁷Lu system can be applied in theragnostics as a multimodal radiotherapy-PDT-imaging system (imaging by SPECT or Cerenkov) and in hypoxic solid tumors in which external radiation is not effective and ¹⁷⁷Lu-CR acts as light source.

A Multimodal Theranostic System Prepared from High-Density Lipoprotein Carrier of Doxorubicin and 177Lu

Recently, it was demonstrated that doxorubicin (Dox.HCl), a chemotherapeutic agent, could be photoactivated by Cerenkov radiation (CR). The objective of the present work was to develop a multimodal chemotherapy-radiotherapy-photodynamic therapeutic system based on reconstituted high-density lipoprotein (rHDL) loaded with Dox.HCl and ¹⁷⁷Lu-DOTA. ¹⁷⁷Lu acts as a therapeutic radionuclide and CR source. The system can be visualized by nuclear imaging. Fluorescence microscopy showed that rHDL-Dox specifically recognized cancer cells (T47D) that are positive for SR-B1 receptors. Encapsulated Dox.HCl was released into the cells and produced reactive oxygen species when irradiated with a 450-nm laser (photodynamic effect). The same effect occurred when Dox.HCl was irradiated by ¹⁷⁷Lu CR. Through in vitro experiments, it was confirmed that the addition of ¹⁷⁷Lu-DOTA to the rHDL-Dox nanosystem did not affect the specific recognition of SR-B1 receptors expressed in cells, or the cellular internalization of ¹⁷⁷Lu-DOTA. The toxicity induced by the rHDL-Dox/¹⁷⁷Lu nanosystem in cell lines with high (T47D and PC3), poor (H9C2) and almost-zero (human fibroblasts (FB)) expression of SR-B1 was evaluated in vitro and confirmed the synergy of the combined chemotherapy-radiotherapy-photodynamic therapeutic effect; this induced toxicity was proportional to the expression of the SR-B1 receptor on the surface of the cells used. The HDL-Dox/¹⁷⁷Lu nanosystem experienced uptake by tumor cells and the liver-both tissues with high expression of SR-B1 receptors-but not by the heart. ¹⁷⁷Lu CR offered the possibility of imparting photodynamic therapy where laser light could not reach.

[99mTc-HYNIC-N-dodecylamide]: a new hydrophobic tracer for labelling reconstituted high-density lipoproteins (rHDL) for radioimaging

Despite the widespread use of nanotechnology in radio-imaging applications, lipoprotein based delivery systems have received only limited attention so far. These studies involve the synthesis of a novel hydrophobic radio-imaging tracer consisting of a hydrazinonicotinic acid (HYNIC)-N-dodecylamide and 99mTc conjugate that can be encapsulated into rHDL nanoparticles (NPs). These rHDL NPs can selectively target the Scavenger Receptor type B1 (SR-B1) that is overexpressed on most cancer cells due to excess demand for cholesterol for membrane biogenesis and thus can target tumors in vivo. We provide details of the tracer synthesis, characterization of the rHDL/tracer complex, in vitro uptake, stability studies and in vivo application of this new radio-imaging approach.

Preclinical Biokinetic Modelling of Tc-99m Radiophamaceuticals Obtained from Semi-Automatic Image Processing

The aim of this study was to develop a semi automatic image processing algorithm (AIPA) based on the simultaneous information provided by X-ray and radioisotopic images to determine the biokinetic models of Tc-99m radiopharmaceuticals from quantification of image radiation activity in murine models. These radioisotopic images were obtained by a CCD (charge couple device) camera coupled to an ultrathin phosphorous screen in a preclinical multimodal imaging system (Xtreme, Bruker). The AIPA consisted of different image processing methods for background, scattering and attenuation correction on the activity quantification. A set of parametric identification algorithms was used to obtain the biokinetic models that characterize the interaction between different tissues and the radiopharmaceuticals considered in the study. The set of biokinetic models corresponded to the Tc-99m biodistribution observed in different ex vivo studies. This fact confirmed the contribution of the semi-automatic image processing technique developed in this study.

Comparative Effect Between Laser and Radiofrequency Heating of RGD-Gold Nanospheres on MCF7 Cell Viability

Gold nanoparticles conjugated to cyclo-[Arg-Gly-Asp-D-Phe-Lys(Cys)] peptides (AuNP-c[RGDfK(C)]) have been reported as systems with specific cell internalization in breast cancer cells. AuNPs have also been proposed as localized heat sources for cancer treatment using laser irradiation or radiofrequency (RF). The aim of this research was to analyze, based on the Mie theory, the AuNP-c[RGDfK(C)] absorption cross-sections (C(abs)) of low-frequency electromagnetic waves (13.56 MHz, λ = 22 m) and optical frequency waves (laser at λ = 532 nm) and to compare their effect on MCF7 cell viability as thermal conversion sources in AuNPs (20 nm) located inside cells. Cell viability was assessed in MCF7 cells treated with AuNP-c[RGDfK(C)] or water after exposure to the RF field (200 W, 100 V/cm) or laser irradiation (Irradiance 0.65 W/cm2). In both cases (RF and laser) the presence of nanoparticles in cells caused a significant increase in the temperature of the medium (RF: AT = 29.9 ± 1.7 degrees C for AuNP compared to ΔT = 13.0 ± 1.4 degrees C for water; laser: ΔT = 13.5 ± 0.7 degrees C for AuNP compared to 3.3 ± 0.5 degrees C for water). Although RF induced a higher increase in the temperature of the medium with nanoparticles, the largest effect on the cell viability was produced by laser when nanoparticles were located inside the cells (8.7?0.7% for laser compared to 19.4 ± 0.9% for RF). The differences obtained in C(abs) values (laser: 3.7 x 10- (16) m2; RF: 7.9 x 10-(23) m2) and the observed effect on MFC7 cell viability support two mechanisms previously proposed "wave energy absorption by AuNPs" when laser is used as a thermal conversion source, and "attenuation of the wave passing through the AuNP suspension" when RF is applied. The AuNP-c[RGDfK(C)] nanosystem shows suitable properties to improve hyperthermia treatments under laser irradiation due to a larger heat release inside cells.

A freeze-dried kit formulation for the preparation of Lys(27)(99mTc-EDDA/HYNIC)-Exendin(9-39)/99mTc-EDDA/HYNIC-Tyr3-Octreotide to detect benign and malignant insulinomas

About 90% of insulinomas are benign and 5%-15% are malignant. Benign insulinomas express the glucagon-like peptide-1 receptor (GLP-1R) and low levels of somatostatin receptors (SSTR), while malignant insulinomas over-express SSTR or GLP-1R in low levels. A kit for the preparation of Lys(27)((99m)Tc-EDDA/HYNIC)-Exendin(9-39)/(99m)Tc-EDDA/HYNIC-Tyr(3)Octreotide was formulated to detect 100% of insulinomas. The formulation showed radiochemical purity of 97±1%, high stability in human serum, and GLP-1R and SSTR affinity. The biodistribution and imaging studies demonstrated properties suitable for its use as a target-specific agent for the simultaneous molecular imaging of GRP-1R- and/or SSTR-positive tumors.

Two Novel Nanosized Radiolabeled Analogues of Somatostatin for Neuroendocrine Tumor Imaging

The somatostatin receptors (SR), which are overexpressed in a majority of neuroendocrine tumors, are targets for radiopeptide-based imaging using for example the 99mTc-Tyr3-Octreotide peptide. Dendrimers are hyperbranched polymeric structures. The nanoscopic size and near-monodisperse nature properties give polyamidoamine (PAMAM) dendrimers an edge over linear polymers in the context of drug delivery. Gold nanoparticles (AuNPs) conjugated to peptides produces stable multimeric systems with target-specific molecular recognition. The aim of this research was to prepare two nanosized multimeric systems for neuroendocrine tumor imaging, 99mTc-PAMAM-Tyr3-Octreotide and 99mTc-AuNP-Tyr-Octreotide, and to compare their in vitro uptake in SR-positive AR42J cancer cells as well as their biodistribution profile in athymic mice bearing AR42J tumors. [Tyr3, Lys(Boc)5]-Octreotide was conjugated to the carboxylate groups of the PAMAM dendrimer (G3.5) with further Boc deprotection using TFA. 99mTc labeling was carried out by a direct method. 99mTc-Tyr3-Octreotide was conjugated to AuNPs (20 nm) by spontaneous reaction with the thiol group of cysteine. Radiochemical purity (RP) was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in AR42J cancer cells. Biodistribution studies were accomplished in athymic mice with AR42J-induced tumors with blocked and unblocked receptors. Elemental analysis demonstrated that 26 Tyr3-Octreotide molecules were successfully conjugated to one molecule of PAMAM. RP for both nanosized conjugates was > 94% and showed recognition for SR in AR42J cells. The tissue distribution of radioactivity 2 h after 99mTc-PAMAM-Tyr3-Octreotide administration in mice showed specific tumor uptake (4.12 ± 0.57% of injected dose/g) and high accumulation in the pancreas (15.08 ± 3.11% of injected dose/g) which expresses SR. No significant difference in the tumor uptake was found between 99mTc-PAMAM-Tyr3-Octreotide and 99mTc-AuNP-Tyr3-Octreotide. However, the dendrimer-peptide conjugate showed a significant renal excretion. Both radiopharmaceuticals demonstrated properties suitable for use as target-specific agents for molecular imaging of tumors that overexpressed SR.

Calcitriol reduces thrombospondin-1 and increases vascular endothelial growth factor in breast cancer cells: implications for tumor angiogenesis

Calcitriol, a potent antineoplastic vitamin D metabolite, inhibits proliferation, induces apoptosis and slows the growth of tumors. Calcitriol also may exert either antiangiogenic or proangiogenic effects depending on the tissue. Vascular endothelial growth factor (VEGF) and thrombospondin-1 (Tsp-1) are key factors involved in promoting and inhibiting angiogenesis, respectively. The effects of calcitriol on Tsp-1 have not been studied in the mammary gland, while VEGF regulation is not clear, since opposite outcomes have been demonstrated. Therefore, the present study was undertaken to investigate the effects of calcitriol on VEGF and Tsp-1 expression in primary breast tumor-derived cells and a panel of established breast cancer cell lines. In vivo studies in athymic mice were also performed in order to gain further insight into the biological effects of calcitriol on angiogenesis. Real time-PCR and ELISA analyses showed that calcitriol stimulated VEGF mRNA expression and protein secretion while elicited the opposite effect on Tsp-1 in 7 out of 8 cell lines studied, independently of the cell phenotype (P<0.05 in n=5). In vivo, calcitriol significantly inhibited the relative tumoral volume after 4 weeks of treatment; however, serum VEGF was higher in calcitriol-treated animals compared to controls (P<0.05). The integrated fluorescence intensity analysis of CD31, a vessel marker, showed that xenografted breast cancer cells developed tumors with similar vascular density regardless of the treatment. Nevertheless, larger necrotic areas were observed in the tumors of calcitriol-treated mice compared to controls. Since the antineoplastic activity of calcitriol has been consistently demonstrated in several studies including this one, our results suggest that the antitumoral effect of calcitriol in vivo involve different mechanisms not necessarily related to the inhibition of tumor vascularization. Overall, our findings indicate that calcitriol can impact the angiogenic process in breast cancer by regulating VEGF and Tsp-1 expression. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Multimeric system of 99mTc-labeled gold nanoparticles conjugated to c[RGDfK(C)] for molecular imaging of tumor α(v)β(3) expression

Integrin α(V)β(3) plays a critical role in tumor angiogenesis and metastasis. Suitably radiolabeled cyclic RGD peptides can be used for noninvasive imaging of α(V)β(3) expression. The aim of this research was to prepare a multimeric system of technetium-99m-labeled gold nanoparticles conjugated to c[RGDfK(C)] and to evaluate its biological behavior as a potential radiopharmaceutical for molecular imaging of tumor angiogenesis. Hydrazinonicotinamide-GGC (HYNIC-GGC) and c[RGDfK(C)] peptides were synthesized and conjugated to gold nanoparticles (AuNP, 20 nm) by means of spontaneous reaction of the thiol groups of cysteine. The nanoconjugate was characterized by TEM, FT-IR, UV-vis, XPS, and Raman spectroscopy. To obtain (99m)Tc-HYNIC-GGC-AuNP-c[RGDfK(C)] ((99m)Tc-AuNP-RGD), the (99m)Tc-HYNIC-GGC radiopeptide was first prepared and added to 1.5 mL of AuNP solution (1 nM) followed by c[RGDfK(C)] (10 μL, 50 μM) at 18 °C with stirring for 15 min. Radiochemical purity (RP) was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in α(V)β(3) receptor-positive C6 glioma cancer cells. Biodistribution studies were accomplished in athymic mice with C6-induced tumors with blocked and nonblocked receptors, and images were obtained using a micro-SPECT/CT. TEM and spectroscopy techniques demonstrated that AuNPs were functionalized with peptides. RP was 96 ± 2% without postlabeling purification. (99m)Tc-AuNP-RGD showed specific recognition for α(V)β(3) integrins expressed in C6 cells, and 3 h after i.p. administration in mice, the tumor uptake was 8.18 ± 0.57% ID/g. Micro-SPECT/CT images showed evident tumor uptake. (99m)Tc-AuNP-RGD demonstrates properties suitable for use as a target-specific agent for molecular imaging of tumor α(V)β(3) expression.

(99m)Tc-labelled gold nanoparticles capped with HYNIC-peptide/mannose for sentinel lymph node detection

The aim of this research was to prepare a multifunctional system of technetium-99m-labelled gold nanoparticles conjugated to HYNIC-GGC/mannose and to evaluate its biological behaviour as a potential radiopharmaceutical for sentinel lymph node detection (SLND).

METHODS

Hydrazinonicotinamide-Gly-Gly-Cys-NH(2) (HYNIC-GGC) peptide and a thiol-triazole-mannose derivative were synthesized, characterized and conjugated to gold nanoparticles (AuNP, 20 nm) to prepare a multifunctional system of HYNIC-GGC-AuNP-mannose by means of spontaneous reaction of the thiol (Cys) present in HYNIC-GGC sequence and in the thiol-mannose derivative. The nanoconjugate was characterized by transmission electron microscopy (TEM), IR, UV-Vis, Raman, fluorescence and X-ray photoelectron spectroscopy (XPS). Technetium-99m labelling was carried out using EDDA/tricine as coligands and SnCl(2) as reducing agent with further size-exclusion chromatography purification. Radiochemical purity was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in rat liver homogenized tissue (mannose-receptor positive tissue). Biodistribution studies were accomplished in Wistar rats and images obtained using a micro-SPECT/CT system.

RESULTS

TEM and spectroscopy techniques demonstrated that AuNPs were functionalized with HYNIC-GGC-NH(2) and thiol-mannose through interactions with thiol groups and the N-terminal amine of cysteine. Radio-chromatograms showed radiochemical purity higher than 95%. (99m)Tc-EDDA/HYNIC-GGC-AuNP-mannose ((99m)Tc-AuNP-mannose) showed specific recognition for mannose receptors in rat liver tissue. After subcutaneous administration of (99m)Tc-AuNP-mannose in rats (footpad), radioactivity levels in the popliteal and inguinal lymph nodes revealed that 99% of the activity was extracted by the first lymph node (popliteal extraction). Biodistribution studies and in vivo micro-SPECT/CT images in Wistar rats showed an evident lymph node uptake (11.58 ± 1.98 %ID at 1 h) which was retained during 24 h with minimal kidney accumulation (0.98 ± 0.10 %ID) and negligible uptake in all other tissues.

CONCLUSIONS

This study demonstrated that (99m)Tc-AuNP-mannose remains within the first lymph node during 24 h and therefore might be useful as a target-specific radionanoconjugate for SLND using "1-day" or "2-day" conventional protocols.

Lys3-bombesin conjugated to 99mTc-labelled gold nanoparticles for in vivo gastrin releasing peptide-receptor imaging

The gastrin releasing peptide-receptor (GRP-r) is over-expressed in breast and prostate cancer and lymph node metastases. Lys3-bombesin is a peptide that binds with high affinity to GRP-r. The aim of this research was to prepare a multifunctional system of technetium-99m labelled gold nanoparticles conjugated to Lys3-bombesin/HYNIC-GGC and to evaluate its biological behaviour as a potential radiopharmaceutical for in vivo GRP-r imaging.

METHODS

Lys3-bombesin and hydrazinonicotinamide-Gly-Gly-Cys-NH2 (HYNIC-GGC) peptides were conjugated to gold nanoparticles (AuNP, 20 nm) to prepare a multifunctional system of HYNIC-GGC-AuNP-Lys3-bombesin by means of spontaneous reaction of the thiol (Cys) present in HYNIC-GGC sequence and the amine of Lys3-bombesin. The nanoconjugate was characterized by transmission electron microscopy (TEM), IR, UV-Vis, Raman, and X-ray photoelectron spectroscopy (XPS). Technetium-99m labelling through the HYNIC-GGC ligand was carried out using EDDA/tricine as coligands and SnCl2 as reducing agent with further size exclusion chromatography purification. Radiochemical purity was determined by size exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in human prostate cancer PC-3 cells (GRP-r positive cells). Biodistribution studies were accomplished in athymic mice with PC-3 induced tumours and images obtained using a micro-SPECT/CT system.

RESULTS

TEM and spectroscopy techniques demonstrated that AuNPs were functionalized with HYNIC-GGC-NH2 and Lys3-bombesin through interactions with thiol groups of Cysteine and the N-terminal and epsilon-amine of Lysine respectively. Radio-chromatograms showed radiochemical purity higher than 95%. 99mTc-EDDA/HYNIC-GGC-AuNP-Lys3-bombesin (99mTc-AuNP-Lys3-bombesin) showed specific recognition for GRP-r over-expressed in PC-3 cells. After administration of 99mTc-AuNP-Lys3-bombesin in mice the pancreas-to-blood ratio was 36 at 1 h demonstrating ability to target in vivo GRP receptor-bearing cells. In vivo micro-SPECT/CT images in mice showed an evident tumour uptake (6.39 +/- 0.83% IA/g at 1 h).

CONCLUSIONS

This study demonstrated that the 99mTc-AuNP-Lys3-bombesin multifunctional system shows specific recognition for GRP-r and suitable properties to be used as a molecular imaging agent.

Peptides for in vivo target-specific cancer imaging

Molecular imaging comprises non-invasive monitoring of functional and spatiotemporal processes at molecular and cellular levels in living systems. Advanced imaging techniques can monitor such processes. Peptide receptors over-expressed in tumours can be targeted by peptides conjugated to radionuclides, near-infrared fluorochromes, metallic nanoparticles or quantum dots for target-specific cancer imaging.